Why does the amount of device utilization vary from one version of software to another?
With every release of software, there are changes to synthesis and fitting algorithms to improve the quality of results. There are times where an optimization in synthesis does not yield improved results in 100% of the designs. The same occurs with fitter algorithm improvements. This can lead to device utilization changing slightly from one software release to the next.
To minimize the differences, ensure that the same synthesis and fitting options are used when comparing the two versions. It is possible that some default options changed between versions.
For other common CPLD questions, see the CPLD FAQ: (Xilinx Answer 24167).